Royal Microscojncal Society. 263 



I suspect tliem to retain tlieir freshness and be capable of effecting 

 such changes on the semi-sohd material within, as shall keep the 

 scale in its normal state, especially as relates to the pigmented scales 

 in Lepidoptera, Mr. Wenham notices the scales of Lepidocyrtus 

 are limp as wet paper, and certainly it is difl&cnlt to unbend them 

 without damage when folded. 



I would willingly cede these points, was it not deemed that the 

 pigmented scales require a fuller examination than they have yet 

 received at our hands. 



How much of the iridescence of the scale may be due to hght 

 reflected from a finely-ribbed surface, or from interference and 

 diffraction in its passage through u-regularly-refracting portions, 

 occasioned by the inner framework, or to the fine pigment granules 

 in the substance of the scale, or to the pigmentary granular deposit 

 on the free surface, is doubtful ; but we must not overlook the fact 

 that where the pigmentary layer has been accidentally or purposely 

 removed, the chromatic effects are yet very perfect under oblique 

 illumination. It is assumed the pigment material largely determines 

 the general colour of the scale, as yellow, green, brown, blues, reds, 

 &c., of all shades, and the pearly or opaque white by reflected light, 

 perhaps by absorption. 



For it was noticed, heat in charring the scale altered its colour 

 to the naked eye, most completely in the very iridescent scales, 

 while under the microscope their structure was not proportionately 

 changed, unless the torrefying had been carried to extremes when 

 parts were often displaced. 



How much of the colour may be due to interference or the pas- 

 sage of the light through the object traversing substances capable 

 of affecting the velocities, bending them out of their course, more or 

 less diffracting or breaking them up into prismatic rays, and these 

 again suffering refraction and reflexion in various ways ; to at last 

 meet with rays of certain velocities, which either swell their amount 

 of colour, or interfere by want of harmony in their undulations, and 

 either reduce them or modify them, so as to furnish several com- 

 pound colours in all parts of the object, of more or less corresponding 

 power over the original light, and with interference shadows in 

 addition, is a question open to considerable doubt, if not defying 

 human skill. 



And when the phenomena of colour in its complementary cha- 

 racters embrace more than two colours, due in part to the nature 

 of the object and in part to the final corrections given to the ob- 

 jective by the optician, the subject becomes much confused by 

 furnishing a mixture of interference spectra, very charming to the 

 eye, as in Figs. 5 and 26 i, but useless in the analysis of structure. 

 Yet if the adjacent parts be not sacrificed in definition, an additional 

 aid may be found for increasing our knowledge of intimate struc- 



